1. Field
This application relates to optical fibers in general and to photonic bandgap fibers in particular. Some aspects of this application are directed towards a photonic bandgap fiber having increased transmission bandwidth.
2. Description of Related Art
Hollow core (HC) photonic bandgap fibers (PBGF) can be useful for many applications. Light in hollow core photonic bandgap fibers is substantially confined to a hollow core by a photonic bandgap in the cladding structure. Because light is largely guided in the air in hollow core PBGFs, high nonlinear thresholds can be obtained. The high nonlinear threshold as a result of light guided mostly in air provides for a wide range of applications. For example, high energy pulse compression and wavelength-tunable Raman solutions are some possible applications that have been demonstrated recently. Transmission, delivery and shaping of optical pulses with very high peak powers are also possible in such fibers. HC PBGFs can also be useful for spectroscopy of gases due to the increase in interaction length when light is in a low loss guided mode.
HC PBGFs with hexagonally arranged cladding structures have been demonstrated and studied in the last decade. HC PBGFs having low loss, for example approximately 1 dB/km, and having a bandgap of approximately 300 nm centered around 1550 nm have been previously reported. In some embodiments, the limited width of the bandgap can be a practical constraint. For example, in some embodiments, the center of the bandgap may need to be carefully controlled to provide the correct transmission characteristic at a pre-determined wavelength. In some embodiments, the bandgap width can also be important for applications that require low third order dispersion, such as pulse shaping, and for applications which require wide bandgaps for new wavelength generation and spectroscopy.